A wide assortment of implantable medical devices are presently known and commercially available. These implantable medical devices include a variety of implantable cardiac devices. For example, implantable pulse generators (IPGs) are a type of cardiac device that is generally used to elevate the heart rate that is beating too slow. This type of device is sometimes referred to as a Bradycardia device or a pacemaker. Another type of implantable cardiac device is implantable cardiac defibrillators (ICDs). This type of device, often referred to as a Tachycardia device, is generally used to provide burst pacing pulses or a defibrillators shock to the heart when the heart is beating too fast. Another type of device is a cardiac resynchronization device used to treat heart failure.
Most implantable medical devices are contained within a hermetically sealed enclosure, in order to protect the operational components of the device from the harsh in-vivo environment, as well as to protect the body from the device. Typically it is necessary to provide an implantable medical device with a source of power, e.g., a battery, housed within the hermetic enclosure of the device. Battery longevity is often a critical consideration in the design and implementation of body implantable devices. It is highly impractical to replace the battery of the implanted medical device and it is clearly desirable to require replacement of the implanted device—a surgical procedure—as infrequently as possible.
Furthermore, notwithstanding the various measures that can be taken to maximize battery longevity, battery depletion is inevitable and many implantable medical devices are designed to account for this. For example, many implantable medical devices are provided with the ability to communicate an “elective replacement indicator” (ERI). The ERI informs the clinician that the device's power supply is nearing, but has not yet reached end-of-life (EOL), the point at which the power supply cannot provide sufficient energy to keep the device operable. The advance warning provided by an ERI gives the clinician the opportunity to take appropriate measures, e.g., to replace the device prior to EOL. Additionally, the implantable medical device may itself turn off various features, processors or therapies to save power in response to the ERI.
One current problem with implantable medical devices is that the ERI predictor may in some cases incorrectly indicate that replacement does not need to occur when it in fact it does. In other cases, the ERI predictor may indicate that replacement needs to occur when it does not. This is generally the case where the ERI is based on statistical calculations and various battery depletion metrics that have a relatively high degree of error between the prediction and the actual ERI event. This incorrect estimation of the battery life can lead to unexpected loss of device functionality which may be a serious medical event. Other errors may lead to premature replacement of the device.
Thus, what is needed is an improved, accurate system and method determining when to replace an implantable medical device.